As the US celebrates St Patrick's Day, a race row has erupted over controversial claims that Irish people were the first slaves to be transported to the Americas and that their suffering was as bad as anything endured by Africans. Although not given much credence by serious historians, some Irish people have used the claims to attack movements like Black Lives Matter, and in turn are accused of attempting to diminish the history of slave trade.

The claims about Irish slaves were first made in a 2007 book, "White Cargo", by authors Don Jordan and Michael Walsh. The book claims that "from 1641 to 1652, over 500,000 Irish were killed by the English and another 300,000 were sold as slaves. Ireland's population fell from about 1,500,000 to 600,000 in one single decade." Irish slaves were treated worse than Africans, the book says, and could be bought much cheaper.

Now an article based on the book has been published by a website called Global Research, and also shared on Irish diaspora website Irish Central, and has been viewed over a million times. "Irish Lives matter" memes have also started circulating.

However Irish historian Liam Hogan says the claims are "ahistorical" and bear no comparison with the African slave trade. "Historically, the majority of Irish prisoners of war, vagrants and other victims of kidnapping and deception – thought to have numbered around 10,000 people – were forcibly sent to the West Indies in the 1650s," said Hogan. "Those that survived were pardoned by Charles II in 1660.

"In contrast, the transatlantic slave trade lasted for four centuries, was the largest forced migration in world history, involving tens of millions of Africans who were completely dehumanised, and its poisonous legacy remains in the form of anti-black racism. So this neo-Nazi propaganda is false equivalency on an outrageous scale."

Other historians have pointed out that the Irish were also involved in the slave trade – as traders and even owners. Even if the figures are accurate, the number of Irish "slaves" is small compared with the estimated 12 million Africans shipped across the Atlantic, as well as to Europe and Muslim countries.

However another aspect to the debate about slavery – and possible reparations – is that by some estimates, over a million people were snatched from European boats and even the coast of places like England and Ireland by slave traders from North Africa in the 17th century. Many ended up in countries like Algeria, though precise figures are impossible to verify.